This guide provides an updated look at calculating the critical resistor values for the LM3915 to ensure your LED display is perfectly calibrated for both brightness and voltage range. 1. Key Formulas for Circuit Calibration
resistor in series with the signal input (Pin 5) can protect it up to ±100Vplus or minus 100 cap V : Always place a tantalum or lm3915 calculator updated
) is roughly 1/10th of the current that will flow through each LED. This guide provides an updated look at calculating
VREF=1.25V×(1+R2R1)cap V sub cap R cap E cap F end-sub equals 1.25 cap V cross open paren 1 plus the fraction with numerator cap R 2 and denominator cap R 1 end-fraction close paren : Connected between Pin 7 (REF OUT) and Pin 8 (REF ADJ). : Connected between Pin 8 (REF ADJ) and Ground. Step 2: Calculate LED Current ( ILEDcap I sub cap L cap E cap D end-sub The current flowing out of Pin 7 ( IREFcap I sub cap R cap E cap F end-sub VREF=1
Data sourced from instructional guides at Instructables and SparkFun . 3. Critical Component Selection Tips : It is highly recommended to keep VLEDcap V sub cap L cap E cap D end-sub
The reference voltage determines the "full scale" point—the voltage level required to light up the 10th LED.
ILED≈12.5R1cap I sub cap L cap E cap D end-sub is approximately equal to the fraction with numerator 12.5 and denominator cap R 1 end-fraction For a standard LED current of , should be approximately . If you need brighter LEDs (e.g., 20mA ), reduce to . 2. Practical Design Examples